This study investigated the influence of viscosity and uronic acid composition of alginates on the properties of alginate films and microspheres produced by emulsification. Tensile properties of films were determined while the yield, size, drug contents and release characteristics of the microspheres were examined. Tensile properties of calcium alginate matrix were significantly affected by the orientation and arrangement of the polymer chains. High viscosity alginates gave rise to higher yields and bigger microspheres. Generally, microspheres with high drug content and slower rate of drug release had high Ca2+ contents and were produced from alginates of higher viscosity. Within an alginate microsphere batch, small sized microsphere fractions had higher drug contents but showed faster drug release rates. Microspheres having a defined size range revealed great dependence of encapsulation efficiency and drug release rates on viscosity and extent of Ca2+-alginate interaction. Viscosity appeared to exert a predominant influence on the microsphere properties.